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Loans and Loans Held for Sale - Loans Held for Sale (Detail) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2013
Dec. 31, 2012
Sep. 30, 2012
Mar. 31, 2012
Dec. 31, 2011
Loans [Line Items]          
Commercial, financial and agricultural $ 180 $ 29   $ 28  
Real estate - construction       15  
Commercial lease financing 9 8   30  
Total loans held for sale 434 599 628 511 728
Commercial mortgage [Member]
         
Loans [Line Items]          
Real estate - mortgage 196 477   362  
Residential mortgage [Member]
         
Loans [Line Items]          
Real estate - mortgage $ 49 $ 85   $ 76